1. Field of the Invention
The present invention relates to a method and apparatus for adjusting image depth, and more particularly, to a method and apparatus for adjusting image depth based on image parallax gradient.
2. Description of the Prior Art
With the progression of multimedia technology, users are pursuing stereo/three-dimensional (3D) and realistic image displays. In the present flat panel displays, the ordinary two-dimensional (2D) display method already can not fulfill the demand of pursuing vivid visual experience of users. Since the most vivid visual effect is stereoscopic vision acquired by binocular disparity of human eyes, how to provide different images to each eye via 3D image display such that observers get visual experience with depth becomes one of development focuses at present.
Since objects located at different positions may have various depths, an observer will perceive layering (or called gradation) of 3D effect accordingly. The 3D image display provides separate images to left eye and right eye while an observer utilizing eyes for observing objects wherein left eye and right eye has different vision angles, such that the brain of the observer analyses and superimposes the seen images and senses layering and depth of the objects, so as to perceive a 3D image. In other words, 3D display devices respectively display left-eye image and right-eye image to left eye and right eye of the observer, such that the observer experiences images with 3D effect. Parallax is a difference in the apparent position of an object viewed along two different lines of sight and here parallax is used to represent the difference in position of an object in a 3D image pair measured in pixels. Disparity is the difference in image location of an object seen by the left and right eyes and here disparity is used to represent the difference in position of an object in a 3D image pair seen by the left and right eyes measured in millimeter units (mm).
The same 3D image displayed on different size of display devices will introduce different experienced 3D effects. For example, the larger display screen uses, the larger disparity occurs, and thus, the 3D effect may be too strong. Since a small parallax may result in a large disparity due to the large movie theater screen, a film shooter usually uses a rather small parallax during film shooting, so as to avoid the audience feeling sick and dizzy. However, when the film is displayed on a typical television, the small parallax may result in a weak 3D effect. On the other hand, during television program shooting, a cameraman usually uses simple shooting equipments having a small monitor screen. Thus, the cameraman requires using rather large parallax to obtain a large disparity for making the 3D effect clearly visible on the small monitor screen. However, when the television program with a stronger 3D effect is displayed on a large television, the 3D effect will be too strong. In short, when the depth of 3D image is too strong or too weak during film shooting or television program shooting, or when an observer wants to watch the 3D image in different size of displays, this may result in an uncomfortable view or a weak 3D effect.
The conventional technique usually calculates disparity values according to the maximum value, the minimum value, and the mean value of the parallax values of the 3D image and display size. Furthermore, the calculated disparity value is compared with a predetermined maximum threshold value, predetermined minimum threshold value and predetermined mean threshold value for determining direction of adjustment. Accordingly, the whole left-eye image or the whole right-eye image is shifted together to change depth of the whole 3D image. However, shifting of the whole 3D image cannot change the relative distances among objects in the 3D image, and thus is unable to increase layering of 3D effect. Besides, while calculating image parallax, the image may be divided into multiple blocks and blocks of one frame are compared with blocks of another frame, such that a block matching may be completed to obtain corresponding match blocks on another frame. The distances between blocks on one frame and corresponding match blocks on another frame are regards as the image parallax. However, such a block matching method would incur longer search time and more complex computations, and are thus not suited for real-time applications.